Just bought a new ecu from Vag Parts. Does anyone know if it will need coded to my car or will it just be a case of pluging it in and it will work fine.
Foot to the floor
I have no idea what variant your A3 is but...
Generally speaking you would need to clone the serial eeprom contents (VIN, immobiliser etc) from the old ECU to the new.. or get the dealer to code it.
My car is an A3 Sport '98. Will the car start though so that I can drive the car to audi?
I doubt it will start without you coding it to the Immo.
You will at least need to plug it in and tell the immo its a new ecu using vagcom or similar just to get the car moving